Coperas or Copperas: How To spell?

The word Coperas is misspelled against Copperas, a noun meaning "Green vitriol, or sulphate of iron; a green crystalline substance, of an astringent taste, used in making ink, in dyeing black, as a tonic in medicine, etc. It is made on a large scale by the oxidation of iron pyrites. Called also ferrous sulphate."